The present invention relates to cables containing optical fibers and more specifically to such cables where the optical fibers run substantially parallel to the cable and to a support or strengthening member within the cable. The present invention also relates to an apparatus and method for fabricating cables containing optical fibers where the optical fibers run substantially parallel to the cable and the support member of the cable.
Optical fibers, sometimes called fiber optics, are signal transmitting media that transmit light signals faster and with less distortion than electrically conductive wires transmit electrical signals. Because of these characteristics optical fibers are a desireable transmission medium. Optical fibers are constructed with two sections: a central core and a cladding which surrounds the core. The central core is made of a material that transmits light and the cladding is made of a material that has a lower refractive index than the central core. The difference in the refractive index of the two materials causes a condition of total internal reflection within the optical fiber. Total internal reflection causes a major portion of a transmitted signal to be reflected and transmitted within the central core. A major problem with optical fibers is that they are very fragile and therefore are damaged very easily.
The prior art discloses cables in which the optical fibers are wrapped in a helical shape around a central support member and imbedded in a protective covering. A function of this structure is to protect the fragile fibers. See FIG. 1 labeled PRIOR ART. For example, U.S. Pat. No. 4,156,104 to Mondello discloses a submarine cable for optical communications which utilizes helically oriented optical fibers. There are a number of problems associated with cables utilizing helically oriented optical fibers.
By forming cables in which optical fibers are wrapped in a helix, the optical fiber may be damaged or attenuated. Damage or attenuation of an optical fiber may result in distortion and/or attenuation of any signals sent through the fiber. Distortion of a signal is problematic since it necessitates adding filters to the receiving apparatus to obtain the true signal. It is also problematic since, in some cases, a signal may be distorted to such an extent that no amount of manipulation of the received signal can recover the true signal. Attenuation of a signal is problematic in that more booster stations are needed to transmit an attenuated signal. Since booster stations are very expensive, attenuation of a signal increases the cost of building a system which relies on optical fibers to carry a signal.
Another problem with cables using helically oriented optical fibers is that the helical orientation necessitates the use of a longer length of optical fiber than the length of cable into which it is placed. This is problematic since optical fibers are expensive. Therefore, it is desirable to reduce the amount of optical fibers required for a given length of cable.
Another problem with the prior art involves the method in which cables which utilize optical fibers are fabricated. Prior to the present invention such cables were fabricated in a multi-step process: i.e. the optical fibers were wrapped around a central core then the protective coating was applied over the cable. A multi-step process increases the cost of fabricating cables which utilize optical fibers.